a. Field of the Invention
This invention relates generally to woodworking tools and specifically tools for use in guiding the boring of dowel holes.
B. Description of the Prior Art
A common requirement in woodworking is the joining of a first work piece, such as a wood board, to a second work piece, using dowels to strengthen the joint. In drilling the dowel holes in the respective work pieces, maintaining precise relative spatial relation between dowel holes is essential since even minor misalignment of opposed dowel holes will result in a gap between the work pieces when joined, thereby weakening the joint and damaging the esthetic appearance of the finished work.
Numerous prior art devices are available which provide for the boring of adequately aligned dowel holes when joining, for example, the edge or end of a first work piece to the edge or end of a second work piece. However, many other common dowel hole drilling requirements are unsatisfactorily solved by the prior art devices. One such common requirement is the joining of the end of a first work piece to the lateral dimension of second work piece, transversely thereto. An example of this requirement is the attachment of a horizontal shelf member intermediate the ends of a vertical frame member in the construction of a book shelf.
As taught in U.S. Pat. Nos. 581,811 and 2,583,283, dowel boring guides may be constructed in combination with clamping means for clamping the guides across the width of each work piece, the clamping surfaces contacting opposing edges of the work piece and being substantially in alignment with the proposed location of the dowel holes. While boring dowel holes in the lateral dimension of a work piece, the clamping surfaces contact sufficient surface area to provide stability for the guide; however, when boring dowel holes in the end of a work piece, inadequate surface area is contacted to provide the required support for precision boring, particularly when relatively thin boards are being joined.
Other boring guides known in the prior art, as disclosed in U.S. Pat. Nos. 1,432,485, 1,762,457, and 2,934,979, provide sufficient clamping surface for precision boring in the end or edge of a work piece by contacting the opposed lateral dimensions of the work piece. These prior art devices are not adaptable for guiding the drilling of dowel holes transverse the lateral dimension of a work piece since clamping across the substantial length of the work piece is required and is clearly prohibitive.
A second source of misalignment inherent in the above referenced prior art is the need to reposition a single cylindrical tool opening such that multiple dowel holes may be bored. The requisite indexing of the boring guide is an obvious source of misalignment. The latter problem is solved to some degree by U.S. Pat. No. 2,930,263 wherein the dowel hole boring guide includes a block containing a plurality of tool openings. However, the configuration of this referenced device is adapted for guiding the boring holes in the ends and edges of work pieces only--not transverse the width intermediate the ends.
A second catagory of doweled joints wherein the prior art devices are unsatisfactory is the drilling of dowel holes in the beveled or angular ends of work pieces, for example, when joining the ends of work pieces to form a skirt or support for a pentagonal or other polygonally shaped table. Again, the problem is that of providing secure clamping support while assuring precise relative spatial alignment of the opposed dowel holes.
As taught in U.S. Pat. No. 2,260,784, dowel boring guides may be constructed in combination with clamping devices whereby shims and spacers may be interposed between the clamping surfaces and the sides of the work pieces, thereby securing the work piece in proper orientation with the dowel hole guide. However, an infinite variety of such shims and spacers would be required in order to provide the capability of matching all possible bevels or angles, an obviously detrimental departure from simplicity of construction.